This invention relates generally to apparatus and methods for making aggregate product from particulate material, and more particularly to apparatus and methods for making an aggregate coal product by compacting or extruding coal particles.
Coal is widely used as a fuel source for generating heat and is often transported over long distances from the mining area to the end user. In order that coal remain an attractive fuel source, it is imperative that means be devised to transport coal efficiently and economically.
Coal fines, which are extremely small coal particles typically having a diameter of about 1 mm or less, are produced in significant quantities by the washing of mined coal and possess a potentially significant heating value. However, their large water content often makes them difficult to handle and use as a fuel source. Currently, because coal fines cannot be dewatered and/or processed into a form which may be easily transported economically, they are usually collected in tailing ponds as a waste product of coal mining or coal preparation operations rather than being recovered. Coal fines represent a significant environmental problem which would be reduced if a process were available which could economically convert coal fines into a usable fuel source.
It has been suggested that mined coal particles, coal fines and other carboniferous particles could be processed into a more easily transportable and usable form by fabricating aggregate products from the particulate material. It is generally known that loose particles of coal can be formed into aggregate products (e.g., various shaped briquettes) by compacting or extruding a mixture of coal particles and a significant amount of a binder additive (e.g., pitch).
In particular, it is contemplated that cylindrical aggregates of coal, otherwise referred to as coal logs, can be easily transported through a hydraulic coal log pipeline, such as that described and shown in U.S. Pat. No. 4,946,317 (Liu et al.). To withstand the rigors of transporting coal logs through the pipeline, the coal logs must be dense and have a high tensile strength to inhibit the coal logs from fragmenting during transport.
Conventional production of coal logs generally involves feeding coal particles mixed with a binder additive into a cylindrical mold and compacting or extruding the coal particles to form a coal log. The end surface of the mold is typically flat, presenting a sharp corner at the mold exit. As the coal log is ejected from the mold, elastic recovery of the coal log causes it to expand rapidly against the sharp corner of the mold exit, creating a high stress concentration in the coal log. A major problem associated with this type of production is the causation of deep circumferential cracks, or even splitting of the coal log into pieces (disks), due to the high stress concentration caused by the sharp cornered mold exit.
Tapered molds are sometimes used in industry to form aggregate products from particulate material. In this type of mold, the inner surface of the mold is tapered from one end of the mold to the other to allow the aggregate product to expand as it exits the mold. However, compacting or extruding particulate material in a mold having a fully tapered inner surface inhibits complete compaction of the particulate material, resulting in aggregate products which are of a lesser quality than products formed in a mold having a straight inner surface. Additionally, a fully tapered mold is impractical for use in forming coal logs because the product formed by the mold is generally conical, and would not travel properly through the coal log pipeline.
There is a need, therefore, for an improved method and apparatus for forming an aggregate product from particulate material, particularly in making coal logs from coal particles. This invention is directed to such a method and apparatus.
Among the several objects and features of the present invention are the provision of an improved mold, apparatus and method for making a stronger, higher quality aggregate product from particulate material; the provision of such a mold, apparatus and method which will produce coal logs having sufficient strength and durability to withstand the rigors of handling and transport; the provision of such an apparatus which recovers water released from the coal within the mold during pressurization; and the provision of such a mold, apparatus and method in which the time required to produce a coal log of increased quality is significantly reduced.
In general, this invention involves a mold for use in making an aggregate product from particulate material. The mold has open ends and an inner surface between the open ends defining, in part, a pressurization chamber for receiving the particulate material so that it may be pressurized to form the aggregate product. The pressurization chamber has a central longitudinal axis, wherein the inner surface of the mold is substantially parallel to the central longitudinal axis. One of the open ends of the mold has a flared inner peripheral end surface flaring outwardly away from the pressurization chamber and the central longitudinal axis for allowing expansion of the aggregate product as it is pushed out of the one end of the mold past the flared end surface.
In another aspect, an apparatus for making a coal log from coal particles comprises a frame, a mold supported by the frame having open first and second ends as set forth above, and pressurizing means supported by the frame operable to pressurize the coal particles within the pressurization chamber to form the coal log and to push the coal log out of the first end of the mold past the flared end surface.
In yet another aspect, a method for making a coal log from coal particles comprises loading the coal particles into a mold having an open end and an inner surface defining, in part, a pressurization chamber. The open end has a flared inner peripheral end surface. The coal particles are pressurized within the pressurization chamber such that the coal particles aggregate to form the coal log. The coal log is pushed out of the mold past the flared end surface so that the coal log expands as it passes the flared end surface.
Another aspect of the method of making coal logs from coal particles comprises loading the coal particles into a mold having first and second open ends and an inner surface defining, in part, a pressurization chamber. First and second rams are operated to apply compacting pressures to the coal particles in the pressurization chamber to form the coal log. After the coal log is formed, the compacting pressure applied by the first ram is reduced and the second ram continues to apply a force sufficient to push the coal log out of the mold while the first ram maintains a back pressure on the coal log as it is pushed out of the mold.
Other objects and features will become in part apparent and in part pointed out hereinafter.